Field of the Invention
The present invention relates generally to encapsulated vaccines and methods of making same, and more particularly, to oral vaccines that release an embedded bioactive agent at the site of action along the foregut and hindgut of an animal and the vaccine is embedded in a cross-linked matrix that is protected by a glassy matrix of sugars.
Related Background Art
Many therapeutic agents, particularly vaccines, are mostly delivered through the injectable route, which is traumatic, inconvenient, expensive, and may fail to induce an appropriate immunogenic response in the mucosal tissues of the animal. In fact, most infections begin at the mucosal surfaces, so immunization against these infective agents depends on the successful induction of a mucosal immune response. While parenteral vaccination is effective at eliciting a systemic immunity, oral vaccines can elicit mucosal immunity and also induce systemic immunity by induction of circulatory antibodies. Oral vaccines are also easier to administer and are less expensive to manufacture than conventional vaccines. However, orally delivered bacterins or subunit vaccines have not been proven to be efficacious since the antigens are generally digested or modified by the stomach prior to presentation to the immuno-responsive cells of the gut mucosa. It is recognized that on passage through the stomach, the vaccine antigenic component(s) can be rapidly inactivated by the gastric pH and digestive enzymes, and thus effective systemic assimilation is compromised. A number of approaches have been tested to provide an oral delivery vehicle that would transit the stomach, but most have been unsuccessful at the commercial scale.
Polymer microspheres and lamellar particles (e.g., liposomes) can be employed for mucosal administration of antigens. Because vaccines themselves may not be efficiently recognized and taken up by mucosal lymphocytes, they typically need to be co-administered with penetration enhancers or adjuvants. Different classes of polymer mixtures are known for potential use as mucoadhesives (Malik, Baboota et al. 2007). These include synthetic polymers such as poly (acrylic acid) (PAA), hydroxypropyl methylcellulose and poly-(methylacrylate) derivatives, as well as naturally occurring polymers such as hyaluronic acid and chitosan. Chitosan has been extensively used for a variety of applications as a biomaterial for tissue engineering, wound healing, and as an excipient for drug delivery (Chopra, Mandi et al. 2006; Dang and Leong 2006). Chitosan has occasionally been tested as an adjuvant for mucosal application (Kim, Kim et al. 2007), but it is typically applied directly to a mucosal surface such as intranasal application in order to obtain IgA response in the nasopharyngeal mucosa of terrestrial animals (Kang, Jiang et al. 2007). Chitosan has also been shown to possess useful properties such as non-toxicity, high biocompatibility and non-antigenicity.
Chitosan can be obtained through the deacetylation of chitin, the major compound of exoskeletons in crustaceans. Chitosan [a-(1˜4)-2-amino-2-deoxy-β-D-glucan], a mucopolysaccharide closely related to cellulose, exhibits chemical properties that are determined by the molecular weight, degree of deacetylation, and viscosity. Chitosan can form microparticles and nanoparticles that can encapsulate large amounts of antigens (van der Lubben, Verhoef et al. 2001; Davis 2006). In the acidic environment of the stomach, chitosan retains its positive charges that hold the particle together. It has been shown that ovalbumin loaded chitosan microparticles can be taken up by the Peyer's Patches of the gut associated lymphoid tissue of higher vertebrates. Additionally, after co-administering chitosan with antigens in nasal vaccination studies, a strong enhancement of both mucosal and systemic immune responses in mice was observed (van der Lubben, Verhoef et al. 2001).
As a result of its interesting properties, chitosan has become the subject of numerous scientific reports and patents on the preparation of microspheres and microcapsules. Chitin and chitosan are being extensively used in the pharmaceutical industry (cosmetics, contact lenses, artificial skin, wound dressing), paper making, photography, solid state batteries, waste water treatment, chromatography, dietary supplements and animal feed. Processing techniques for the preparation of chitosan microspheres have been extensively developed since the 1980s. Several processing approaches have been proposed including ionotropic gelation with an oppositely charged, simple or complex coacervation, emulsification/solvent evaporation and, more recently, spray drying (Huang et al. 2003). Chitosan microspheres obtained by spray drying are characterized by high sphericity and specific surface area, which are important parameters for application in the pharmaceutical field (Rege, 2003).
One particular advantage of chitosan is its ability to form a gel matrix with counter-ions such as sodium tripolyphosphate (TPP) (Bodmeier et al. 1989, Shiraishi et al. 1993, Calvo et al. 1997). TPP is a non-toxic and multivalent anion. It can form either intermolecular or intramolecular links between positively charged amino groups of chitosan and negatively charged counter-ion of TPP (Aral and Akbuga 1998; Shu and Zhu 2000).
Against this background, there is a need for an attractive composition and manufacturing method for an oral delivery system that is cost effective, simple to prepare, and also permits prolonged storage stability while maintaining a high loading capacity for the bioactive agent with retention of its in-vivo immunogenicity. Further desirable benefits of the delivery system would include the accurate dosing of bioactive agent, and the ability of stabilizing and protecting the bioactive agent during the manufacturing process itself (e.g. pelleting or extrusion of a food of feed product). It is the objective of the present invention to provide a composition and a manufacturing method to meet these needs.